An electromagnetic actuator for operating a setting member (for example, a cylinder valve of art internal-combustion engine) has at least one electromagnet--but frequently two spaced electromagnets--energizable in a controlled manner. The electromagnet is associated with an armature which is connected with a guide rod and which is further operatively connected with the setting member. Upon energization of the electromagnet the armature is moved into an end position against the force of a resetting spring and the armature again assumes its initial position when the electromagnet is de-energized. In case two electromagnets and thus two resetting springs are used, during alternating energization of the electromagnets, the armature is reciprocated in accordance with the frequency of the alternating energization. The duration of the energization of an electromagnet also determines the period in which the armature is held at the pole face of the respective attracting electromagnet and, accordingly, the setting member which is operated by the armature is held in the respective switching position.
An electromagnetic actuator of the above-outlined type having two electromagnets is used in particular for operating a cylinder valve of an internal-combustion engine. In such a construction the resetting springs, serve as respective opening and closing springs for the cylinder valve. Because of the necessarily large forces required to maintain the cylinder valve in its closed position and, also, to open the cylinder valve against the gas pressure within the engine cylinder, strong compression coil springs are required which are loaded (compressed) parallel to their geometrical central axis. Such an axis, at the same time, represents the line of motion of the armature, and if the setting member is a cylinder valve, such an axis also represents the line of motion of the cylinder valve.
The end faces of a compression coil spring of the above-outlined type have a planar annular configuration to ensure a satisfactory seating of the spring on the associated spring support.
Because of manufacturing tolerances, however, the effective operating path line of the resulting force of the compressed coil springs generally does not coincide with the geometric central axis. As a result, the Force is not evenly distributed over the spring seating surface, but is introduced at a location preferred by the structure. An eccentric location of the point of force introduction causes, in the seating surface of the compression spring, reaction forces which may be demonstrated by the existence of transverse forces and tilting torques. Such torques are transmitted from the spring support to the armature and the armature guide rod and cause, in addition to a rotation of the armature about its axis of motion, a rocking (tilting) motion of the armature transversely to the Line of motion. As an undesired result, the armature strikes the components laterally bordering the armature chamber, and also, stochastic frictional effects are introduced. A rotation of the armature about its longitudinal axis is particularly disadvantageous in actuator constructions in which the armature is not of rotationally symmetrical configuration but is, for example of rectangular outline. Because of such a tilting motion and as a function of the location of force introduction, the release behavior of the armature from the pole face changes as the electromagnet is de-energized.